Ass.Prof.Dr.Mohamed ALsakkaf*Cement Bases and Liners. Cavity preparation in most situations involve the dentin which mostly has been irritated by:1. Caries.2. Mechanical process of cavity preparation.3. Restorative materials.L9 3

*. After removing the affected tissues and completion of cavity preparation, it is important to:1. Try to prevent further irritation.2. Improve the defense capabilities of dentin pulp organ.

*And this can be accomplished by application of intermediary base material.. Sound dentin is the best barriers between restorative material and pulp.The greater the thickness of overlying dentin Bridge the lesser the irritation reaching the underlying pulp.. Conservation of sound dentin during cavity preparation well be beneficial.

*The purpose of pulp insulation is to protect the pulp against:. Thermal shocks.. Chemical constituents from restorative material.. Galvanic shocks.. Microleakage of bacteria and debris.. Penetration of mercury and other metallic ions.

*Ideal requirements of base materials1. It should have adhesive potential to tooth structure (marginal sealing and adaptation to cavity walls).

2. Non-irritant to vital pulp tissues.

*3. Provide thermal insulation against conductive metallic restorations.

4. Reduce galvanic action of metallic restorations.

5. Enhance formation of reparative dentin.

*6. It must be strong enough to withstand condensation forces and future masticatory forces.7. Compatible with overlying restorative materials and other intermediary base material (not react with the material or interfere with its setting reaction).8. It should resist degradation in oral fluids.9. Easy to apply.

*. These ideal requirements should be met to provide the protective and medicating effects on pulp-dentin organ.. No available material provides all these properties so; by combining materials all ideal requirements can be achieved.

*Types and ClassificationsI Cavity LinersA-Cavity Varnishes

. Organic copal resin or synthetic resin gum dissolved in solution of ether chloroform or acetone.

*. These solutions evaporate rapidly after placement on tooth surface, leaving a thin semi-permeable membrane.. Thickness 5-25 depending on the following:1. Type of solvent.2. No. of applications.

*Applications. Applied with small cotton placed in solution (only once to avoid contamination of varnish bottle).. Varnish should be kept in tightly bottle to prevent evaporation of the solvent.

*. The solvent evaporates leaving small pits in the film, so 2 or more layers are indicated.. Remove the excess varnish from external tooth surface by using solvents.. Varnish is insoluble in the oral fluid, so its applied to D + E.

*Uses1. Leakage of oral fluids around the margins and walls at restoration tooth interface.. Reduce postoperative pain and sensitivity.2. In case of amalgam. Retard ion migration into dentin wall result in tooth discoloration.

*3. Dental cement. The semi-permeable nature of varnish film decrease penetration of phosphoric acid from dental cements (Zn / ph and silicate cement) into dentin.

* Remember:. As mentioned varnish applied to E + D walls including cavosurface margins, except at enamel, in silicate cement as it will block the transfer of fluoride from silicate cement [ main reason for selecting this material ].. Contraindicated with G.I as it block the transfer of fluoride and prevent chemical adhesion to tooth structure.

*. Insoluble in dist.water but not used with restorative resins because the gum dissolve in monomer.. Restorative resins containing organic solvents as tooth colored material, destroy the integrity of varnish film rendering it void of value to be used.

* B- Cavity Liners. Ca (OH)2 applied in thin coatings and must be removed from cavity margins.. Ca (OH)2 can neutralize acidity of dental cement.

*Remember. Pt, with recently restored. Complain of pain and discomfort with cold drinks lasts for few seconds (Till takes temp. of mouth).. It lasts for several weeks (not less than 2 and may extend to 2 ms) until the effective barrier of reparative dentin is formed.

*. Pain sensation in dentin is the result of the movement of fluid in d. ts by capillary attraction or by change of osmotic pressure (heating or cooling of dentin).

*II Bases1-Zinc Phosphate Cement. The acidity is quite high at time they are inserted in tooth (PH 3.5), then PH rapidly approaching neutrality during 24 48 hrs, any damage occurs to pulp from Zn / Ph will occur during first few hrs, after insertion.

*. PH is lower and remains lower for long time if thin mixes are employed.. The consistency of the cement is related to Liq.P ratio. ( high powder high thickness of the mix).

*Z.PH. mixes are Prepareda. Luting mix (thin mix) for seating inlays or crowns.b. Base mix (viscous mix).. If luting mix is viscous from the start, it will not permit the flow of the cement beneath casting.

*. Indications1. Replacement of dentin lost by extensive caries to act as:a. Thermal insulating base under metallic restoration.b. Chemical barrier under silicate cements.2. Aid in mechanical retention of gold and porcelain inlays.3. Formation of temporary cement dressing.

*Mixing and insertion1. Mix on a Cool Slap:. Reaction between powder and liquid is exothermic, cool slap to:a. Absorb the heat of the reaction.b. Permits incorporation of a great amount of powder to the desired mix.Leaving the mixed cement on this cool slap during insertion into the cavity, benefits the working time slowing the reaction.

*2. Dispense a Correct P / L Ratio:. By powder dispenser 1 large and 1 small cup of powder are dispensed onto the middle of the slap.. In upper corner additional 2 large cups are dispensed to be used later.. P. of initial large cup divided into 6 equal parts.. Liquid (6-7 drops) dispensed to the side of the divided portions.

*3. Mix Over a Large Area . By long thin bladed steel spatula the first 1\6 portion of powder is mixed with liquid covering at least 1\2 of the slap for 15 sec.. Each portion is spatulated for another 15 sec till inlay consistency is achieved (may require 6 portions) total spatulation time = 90 sec.

*Inlay consistency: when the mass is gathered together and spatula is laid into it and withdrawn cement will string up for 1 1 1\2 inches before breaking. Then mix to heavy putting like consistency.

*Insertion . To prevent sticking of cement to instrument, immerse tapered plugger in the remaining dry powder.. Inlay consistency is used first for better seal + initial retention. Then the heavy consistency mix is placed in area requiring protection.. The cement base is then burnished to place and carved into the desire contour.

*. ZPC (when properly mixed), carried without delay with plastic instrument to the cavity.. Cavity must be dry but not desiccated by alcohol, this increase the chance for phosphoric acid in the cement to be absorbed into dentin, and this lead to pulp irritation.. Cavity varnish can be applied before the cement to minimize acid penetration into pulp.

*. Minimal pressure is applied to spread the cement into place-over pulpal + axial walls only.. Restorative areas + margins of cavity must be free from cement.. Excess cement is removed by sharp excavators and floor is smoothed carefully with inverted cone bur.

*. It has low thermal conductivity, which means good thermal isolator for pulp protection, under metallic fillings.. Phosphate cement increases dentin permeability due to etching by acids.. ZPC is a good base material except for its irritation qualities related to its acid content so:

*1. Cavity varnish is applied first on the floor of moderately deep cavities to minimize the potential harm.

2. Ca(OH)2 as sub-base under Zn / Ph if cavity is deep, because the liner will neutralize the acidity of the cement.

*2 Zinc oxide Eugenol Cement. Used as temporary filling material to seal up cavities between visits to bland the dentin and pulp.It has the Following Pharmacological Actions

*1. Antiseptic action.2. Anti-inflammatory action.3. Counter irritant.4. Sedative action.. It has a perfect initial seal ability, so the prevent ingress of saliva, bacteria and debris into dentin.

*Remember. Through the action of eugenol ring, it will prevent polymerization and Harding of resin material, for this case ZOEC contraindicated as I.B.M if in contact with filled or unfilled materials.. Capable of blocking the penetration of ions from R.M.

*. When used as temporary material, a stiff mix is made on the slap in which small cotton strands are forced into the mix for:a. Reinforcing the mix.b. Easy handling.. The surface is smoothened with moistened, and occlusal relationship are tested and adjusted.

*3. Calcium Hydroxide. Used to cover dentin, forming the floor of deep and moderately deep cavities.. The compounds are alkaline in nature, to enhance secondary dentin formation over pulp (calcific bridge) that seals off the vital tissues against irritation.

*. Used as capping agent (direct or indirect).. It is the material of choice in deep cavities with subsequent pulp exposure (in this case, the material must be applied without pressure).. Not strong enough to provide reliable support for a restoration under heavy occlousal stresses.

*. Strong base of ZPC is used to cover the capping material (Ca(OH)2).. High thermal insulation capacity.. Effective against penetration of acids.. It provided in different forms:1. Powder form.2. Paste.3. Suspension.

*4. Polycarboxylate CementPowder:. Zno and some Mgo.. It may also contain small amounts of Ca(OH)2, fluoride and other salts.

*Liquid:Solution of polyacrylic acid and co-polymers.. More adhesion to tooth structure than any other dental cement.. Produce minimal pulp irritation, despite their initial acidity.. Twice as soluble as Zinc Phosphate cement.. Tensile strength higher than Zn \ Ph.

*5. Glass Ionomer Cement. Based on polyacrylic acid formulation.. Extension of Zinc polycarboxylate cements.PowderAluminosilicate glass with fluoride salts which provide the leached out fluorides responsible for its anticariogenic properties.

*LiquidPolyacrylic acid which has the potential for chelation with ca++ in tooth structure responsible for adhesive properties of the cement.

*Uses . Because of its biologic kindness and potentials for adherence to Ca of tooth.1. Used primarily as R.M. for treatment of eroded lesions.2. Luting agent.3. Base material (even though the material is very sensitive to water and a dry field is imperative).

*. The powder and liquid are mixed on a paper pad or glass slap using plastic spatula.. G.I.C used in sandwich technique in treatment of caries.